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Inmetallurgy,cold forming orcold working is anymetalworking process in whichmetal is shaped below itsrecrystallization temperature, usually at the ambient temperature at or near room temperature. Such processes are contrasted withhot working techniques likehot rolling,forging,welding, etc.[1]: p.375 The same or similar terms are used inglassmaking for the equivalents; for examplecut glass is made by "cold work", cutting or grinding a formed object.
Cold forming techniques are usually classified into four major groups: squeezing, bending, drawing, and shearing. They generally have the advantage of being simpler to carry out than hot working techniques.
Unlike hot working, cold working causes thecrystal grains and inclusions to distort following the flow of the metal; which may causework hardening andanisotropic material properties. Work hardening makes the metalharder,stiffer, andstronger, but lessplastic, and maycause cracks of the piece.[1]: p.378
The possible uses of cold forming are extremely varied, including large flat sheets, complex folded shapes, metal tubes,screw heads and threads,riveted joints, and much more.
The following is a list of cold forming processes:[1]: p.408
Squeezing:Burnishing •Coining •Extrusion •Forging •Heading •Hubbing •Peening •Riveting •Rolling •Sizing •Staking •Swaging •Thread rolling
Bending: Angle bending • Draw and compression • Flanging •Roll bending •Roll forming •Seaming • Straightening
Shearing:Blanking •Cutoff •Dinking •Piercing •Lancing •Nibbling •Notching •Perforating •Shaving •Sheet metal shear-cutting •Slitting • Trimming
Drawing:Embossing •Ironing •Metal spinning •Sheet metal drawing • Stretch forming •Tube drawing •Wire drawing •Superplastic forming
Advantages of cold working over hot working include:[1]: p.375
Depending on the material and extent of deformation, the increase in strength due to work-hardening may be comparable to that ofheat treating. Therefore, it is sometimes more economical to cold-work a less costly and weaker metal than to hot-work a more expensive metal that can be heat treated, especially if precision or a fine surface finish is required as well.
The cold-working process also reduces waste as compared to machining, or even eliminates withnear-net-shape methods.[1]: p.375 The material savings becomes even more significant at larger volumes, and even more so when using expensive materials, such as copper, nickel, gold, tantalum, and palladium.[2] The saving on raw material as a result of cold forming can be very significant, as is saving machining time. Production cycle times when cold working are very short. On multi-station machinery, production cycle times are even less. This can be very advantageous for large production runs.
Some disadvantages and problems of cold working are:[1]: p.375
The need for heavier equipment and harder tools may make cold working suitable only for large-volume manufacturing.[1]: p.375
The loss of plasticity due to work hardening may require intermediateannealings, and a final annealing to relieve residual stress and give the desired properties to the manufactured object. These extra steps would negate some of the economic advantages of cold forming over hot forming.[1]: p.378
Cold-worked items suffer from a phenomenon known asspringback, orelastic springback. After the deforming force is removed from the workpiece, the workpiece springs back slightly. The amount a material springs back is equal to the yield strain (the strain at the yield point) for the material.[1]: p.376 In more complex cases, springback can be estimated by usingfinite-element elastoplastic analysis andneural-network predictions, in the sense of aReduced Order Model based on Artificial Intelligence (ROM-AI).[3]
Special precautions may be needed to maintain the general shape of the workpiece during cold working, such asshot peening andequal channel angular extrusion.
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